1. Field of the Invention
The present invention relates to a circuit module and more particularly to a circuit module including an isolator.
2. Description of the Related Art
Examples of known isolators include a nonreciprocal circuit device described in Japanese Unexamined Patent Application Publication No. 2006-311455. The nonreciprocal circuit device includes a ferrite having a pair of opposed main surfaces, multiple center electrodes, a pair of permanent magnets having main surfaces opposed to the main surfaces of the ferrite, a circuit board, and a yoke. The center electrodes are formed on the main surfaces of the permanent magnets using conductive films so that the center electrodes cross each other and are insulated from each other, and portions of each center electrode are electrically connected to each other through relay electrodes formed on end surfaces perpendicular to the main surfaces of the ferrite. The ferrite and the permanent magnets are disposed on the circuit board so that the respective main surfaces are substantially perpendicular to the surface of the circuit board. The yoke surrounds the ferrite and the permanent magnets, controlling the leakage of magnetic flux out of the nonreciprocal circuit device.
In the nonreciprocal circuit device described in Japanese Unexamined Patent Application Publication No. 2006-311455, the center electrodes are formed on the main surfaces of the permanent magnets using conductive films, and the main surfaces of the ferrite are interposed between the main surfaces of the permanent magnets. Thus, it is possible to obtain a nonreciprocal circuit device which is easy to manufacture compared to traditional devices formed by winding a metal line and which has good characteristics such as reduced size, increased positional accuracy, and fewer variations in electrical properties.
Meanwhile, nonreciprocal circuit devices including no yoke have been proposed in recent years. This configuration facilitates further downsizing of nonreciprocal circuit devices.
In a nonreciprocal circuit device including no yoke, however, as will be described below, the ferrite-magnet assembly composed of the ferrite and the permanent magnets may drop from the circuit board due to a shock caused by a drop or the like. More specifically, in the nonreciprocal circuit device described in Japanese Unexamined Patent Application Publication No. 2006-311455, the circuit board having the ferrite-magnet assembly mounted thereon is mounted on a mother circuit board and thus constitutes part of a circuit module. In the circuit module, the nonreciprocal circuit device is covered with a metal case disposed on the motherboard. When an electronic apparatus including a circuit module as described above receives a shock caused by a drop or the like, the metal case may become grossly deformed. At that time, the metal case may come into contact with the ferrite-magnet assembly of the nonreciprocal circuit device, which may in turn drop from the circuit board.